This invention relates to a ultrasonic flaw detection apparatus for fully automatic ultrasonic flaw detection by use of an information processing unit, which has gained wide application as one non-destructive test technique for the weld zone of a steel product. More specifically, the present invention is an ultrasonic flaw detection apparatus which first performs preliminary flaw detection for the range required and then performs flaw detection at the position of a flaw if such a flaw is present within the range.
Flaw detection of the weld zone of a steel product is generally carried out by, for example, arranging one or more probes on both sides of the weld zone and moving the probe or probes once in a direction parallel to the longitudinal direction of the weld zone. However, this method involves a problem because flaws in the weld zone or in portions near the weld bond can not always be detected in the most desirable state and hence, the flaw detection tends to be inaccurate. A more advanced method, the so-called "precision flaw detection method" is also practised at present. In this method the above-mentioned preliminary flaw detection is carried out once, and then the probe or probes are returned by manipulation of the probe-scanning mechanism to the position of the weld zone where the flow is judged present, in order to again evaluate the flaw. However, this manipulation of the scanning mechanism must be made manually and is therefore troublesome and time-consuming.
Especially for flaw detection of the weld zone between mating steel bars of a high-storied structure, manipulation of the probe-scanning mechanism becomes very complicated and difficult due to the limited working space, thereby causing various practical difficulties and reducing work safety.